Piston



A. L. NELSON Aug. 11, 1936.

PISTON Original Filed June 22, 1927 2 Sheets-Sheet l A. L. NELSON Aug.11, 1936.

PISTON Original Filed June 22, 1927 2 Sheets-Sheet 2 i wy Imm

Patented Aug; 11, 1936 UNITED STATES PISTON Adolph L. Nelson, Detroit,Mich., assignor to Bohn Aluminum & Brass Corporation, Detroit,

Mich.

Original application June 22, 1927, Serial No.,

200,534. Divided and this application June 9,

1928, Serial No. 284,199

7 Claims.

This invention relates to pistons of the type in which the skirt isbraced by a pair of chordal struts and aims to improve the constructionand method of manufacture of such pistons.

A particular object is the provision of a method of manufacture in whichcasting strains are utilized for giving the parts of the pistona.suitable fit within the cylinder. This is accomplished by firstcasting the skirt about the struts 10 to produce casting strains, thengrinding it and afterward slitting it in such a way as to relievecertain of the strains and cause parts of the skirt to become deformedto the desired extent.

A further object is to improve the construction of the struts to givethem better cast-in joints with the material comprising the rest of thepiston, and to permit them to yield with the expansion and contractionof the piston material. The joints at the ends of the struts arearranged so ,that the neutral points of opposite joints may be given anydesired spacing regardless of the spacing of the main part of the strutbodies.

This case is a division of application No. 200,534, filed June 22, 1927,and is in part a continuation of application No. 643,499, filed June 5,1923 and of application No. 35,703, filed June 8, 1925.

In the drawings:

Fig. 1 is a side elevation of a piston embodying 30 the invention.

Fig. 2 is an elevation partly in section looking from the right of Fig.1.

Fig. 3 is a longitudinal section of the piston. Fig. 4 is a section online 4-4 of Fig. l. 35 Fig. 5 is a section taken through the struts.

Fig. 6 is a. plan of a strut blank before bending. Fig. 7 is a viewsimilar to Fig. 6 showing a modified form of strut.

Fig. 8 shows another .type of strut.

40 Fig. 9 shows further modification of strut structure, partly bent tofinished shape.

Fig. 10 is a section on line Ill-l0 of Fig. 9, after the strut has beenbent to finished shape.

Fig. 11 is a view similar to Fig. 9 of a different 45 form of strut.

Fig. 12 is a secti r pn line l2-l2 of Fig. 11 after the strut has beenbent.

Fig. 13 is a view similar to Fig. 9 of an additional type of strut.

5 Fig. 14 is a section on line Ill-l4 of Fig. 13,

after full bending has been completed.

The piston comprising this invention is preferably formed oflight-weight material, such as an aluminum alloy. and comprises ingeneral a head 55 portion and a skirt portion which are separatedthroughout the major portion of the circumference of the piston but arejoined by vertical piers irliitegral and homogeneous with the head and srt.

The strut used in the piston is made from any 6 suitable material, suchas steel, relatively inexpansible as compared with the piston material,and comprises a fiat, platelike body in formed with an upward extensionII at its central part. Below the extension I I a semi-circular notch l21 is formed in the lower edge of the strut, and apertures l3 are cutthrough the body above the notch i2. These apertures I3 are of such asize that the bar I which separates the apertures, as well as the barsl5 and i6 above and below them are 15 relatively narrow for a purpose tobe hereinafter explained. The struts have slightly flaring ends as at H,and an aperture I8 is cut through the body near the end in such aposition that the bar 19 on the notched side of the body is thinner 20than the bar 20 on the opposite side of the body. The ends of the strutare bent forward along lines C--D (Fig. 9) while extension H is bent tothe rear on line A-B. The strut has a pair of positioning apertures 2|formed through its body.

The pistons are preferably cast in permanent molds, and the first stepin the casting process is to place a pair of struts in position in themold with theirnotched sides uppermost. The apertures 2] are engagedover projections formed on themold to thereby accurately position thestruts and to hold them firmly against movement in any direction. Themolten piston metal is then poured into the mold, which is shaped insuch a way that the metaiflows around the center and ends of the struts,but leaves the intermediate parts free, as will be clear from Fi 1-5.

When the hot metal enters the mold it is very fluid and as it rises itflows readily around the 40 relatively thick bar 20, but it cools veryrapidly and loses its fluidity so that by the ime it reaches the bar l9it would have diificulty in flowing around it to form a perfect joint ifthis bar were not made relatively narrow, as explained above.

As the piston cools after casting, the aluminum shrinks faster than thestrut material, and there is a natural tendency for the aluminum to drawaway from the sides of the strut at its center. By shaping the strut sothat the aluminum surrounds narrow bars of the strut, as l4, l5, IS, thealuminum is held tightly to the sides of the strut by the heavy ties ofaluminum formed about the bars. I

After casting, the piston comprises a head 22, piers 23 depending fromthe head and having piston pin bosses 24 formed therein, a lowercircular portion 25 homogeneous with the piers, and semi-cylindricalbearing portions 26 and 21 located between the pin bosses andhomogeneous with the head and with the circular portion 25.

The differential shrinking of the skirt and strut materials aftercasting sets up certain shrinkage strains and distortion in the skirtowing to the tendency of the strut to resist the skirt shrinkage alongcertain lines, while the skirt shrinkage is unopposed along other lines.As a result the diameter M at the extreme bottom of the skirt (Fig. 4)contracts faster than diameter N due to the effect of the struts inholding the upper part of the skirt out along diameter N, and therebydistorting the lower end of the skirt. a

The next step in the formation of the piston is to sever the upper endsof the semi-cylindrical bearing portions from the head by saw cuts 28,leaving the head free to expand under the heat of operating conditionswithout afl'ecting the bearings portions. The piston is then passedthrough a grinding operation to place the desired finish on the outsideof the skirt surfaces. I

The slots 29 are now out upwardly from the bottom of the skirt into thebearing portion 21. The lower end of each slot is approximately below alateral margin of the bearing portion, and the upper ends of the slotsconverge toward each other and are located above the lower ends of therecesses separating the bearing portion from the piers. Cutting theseslots relieves some of the casting strains and as a result the lowerpart of bearing portion 2! lying between the slots 29 springs outwardlyincreasing slightly the width of the skirt on diameter N, while at thesame time the parts of the circular portion 25 that lie below the pinbosses spring inwardly, thereby decreasing the width of the skirt ondiameter M. If the upper ends of the slots are placed closer togetherthe portion between the slots will be more flexible, while if the slotsare made shorter the bearing portion will spring out less. Theseproportions are designed so that the piston will suit the cylinder fitcondition desired, although generally they are made to give an increaseof about .0035 in. on diameter N and a decrease on diameter M of abouthalf that amount.

The skirt slotting disclosed herein has several important advantages.The method of manufacture is simplified by reason of the fact that theslots can be cut after the grinding operation has been finished. Thepiston can be run with a minimum of power loss due to friction since thebottom of the skirt under the pin bosses is given the much needed extraclearance and the upper part of the skirt can be given a relativelyloose fit in the cylinder, the sprung-out portion preventing pistonslap;

Due to its close fit, the bottom end of the skirt wipes the bore of thecylinder for a considerable portion of its circumference and helps tokeep the oil down.

Referring to Fig. 5 it will be seen that the aluminum of the skirtcompletely surrounds the bar 30 at the end of the strut, and that theneutral points of the joints between the ends of the struts and theskirt fall on the lines e-f and g-h, which lines are closer togetherthan the lines representing the axes of the strut bodies.

By giving a correct length to the curved end of the strut it is possibleto produce a desired rate of skirt expansion regardless of the spacingof the main bodies of the struts, since it is the distance between thelines e--) and g-h, that is an important factor in determining theexpansion 5 rate of the skirt. This structure of the strut end alsocontributes to a better grip between strut and skirt, and helps to letthe metal shrink towards the neutral point of the joint.

The outward bend given to the strut extenl0 sion ll permits the strut toyield with the expansion and contraction of the piston metal and helpsto maintain a tight grip of the pier about the strut.

Fig. 6 shows a modified strut blank in which a 15 plurality of roundholes 3| provide means for forming a firm bond between the piers and thestrut.

The blank of Fig. 7 is similar to that of Fig. 6 except that the endbars have been severed to form a plurality of T heads on each side ofthe strut.

The blank shown in Fig. 13 is similar to that shown in Fig. 9 exceptthat its central part is pierced by three elongated openings 32, thisstructure being useful wherever a wide strut is advisable.

As shown in Fig. 11 a number of apertures 33 may be placed in the endsof the struts to produce a plurality of aluminum ties extending 30around the end bar.

Fig. 8 illustrates a blank for an open frame type of strut in which thecentral part of the horizontal bars are formed thin as at 34 to permit aclose aluminum bond being formed thereabout. The 35 projections 35 helpto anchor the strut against movement in the pier, while the faces 36 areused to locate and hold the strut horizontally in the mold.

I claim:

1. A piston comprising a head, piers depending from the head,cylinder-bearing portions, a pair of struts extending between thecylinder-bearing portions, the intermediate portion of each strut beingembedded in a pier, an extension projecting from the intermediateportion of each strut, each extension being buried in a pier, and beingbent away from the plane of the strut.

2. A piston comprising a head, piers depending from the head,cylinder-bearing portions, a pair of struts extending between thecylinder-bearing portions, the intermediate portion of each strut beingembedded in a pier, an extension projecting upwardly from theintermediate portion of each strut, each extension being buried in apier and being bent outwardly away from the plane of the strut.

3. As an article of manufacture, a piston strut in the form of aplate-like member formed with a semi-circular notch cut in onelongitudinal edge of the strut, the plate-like member being also formedwith an anchorageaperture near each end thereof, the aperture beingnearer the notched longitudinal edge than the other longitudinal edge.

4. A piston strut in the form of a plate-like member having two oppositeanchoring sides formed with anchoring formations, and a third side whichis normally the top side when the strut is installed in a piston, saidthird side having a projecting part which is apertured and bent awayfrom the plane of the main strut body.

5. A piston comprising a head, piers depending from the head andcarrying piston pin bosses, cylinder-bearing portions, a pair of strutsof material less expansible than that of the bearing portions, each endof each strut being anchored to a cylinder-bearing portion, and eachstrut carrying an upward projection which is apertured and buried in apier and lies in a plane at an angle to the plane of the main body ofthe strut.

6. A piston comprising a head, piers depending from the head andcarrying piston pin bosses, cylinder-bearing portions, the head andcylinderbearing portions being formed of light-weight material, a pairof struts of material having a lower rate of thermal expansion than thecylinderbearing psrtions, the middle part of each strut being embeddedin a pier, an extension projecting upwardly from the middle part of eachstrut, each extension being apertured and buried in a pier and beingbent outwardly from the main body of the strut.

7. As an article of manufacture, a piston strut in the form of aplate-like body formed with an extension at the middle of one side, theextension being bent away from the plane of the body.

ADOLPH L. NELSON.

